Storage system and data management method

ABSTRACT

A storage system including: a virtualization apparatus having a control unit, said control unit setting an actual volume for storing data sent from a host apparatus, formed in a storage area provided by a physical disk; and a virtual volume paired with the actual volume, for storing replicated data for the data; and an external storage apparatus having a logical volume that functions as an actual storage area for the virtual volume; and a tape associated with the logical volume, for storing the replicated data; wherein the external storage apparatus has a copy unit for copying the replicated data stored in the logical volume to the tape.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 11/672,172, filedFeb. 7, 2007. This application relates to and claims priority fromJapanese Patent Application No. 2006-277921, filed on Oct. 11, 2006. Theentirety of the contents and subject matter of all of the above isincorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a storage system and a data managementmethod. More specifically, the invention relates to technology forbacking up or restoring data using an externally connected storageapparatus.

2. Description of Related Art

Conventionally, as external storage apparatuses for replicating datasent from general-purpose computers (called host apparatuses), tapelibrary apparatuses using magnetic tape cartridges, and storageapparatuses using volumes logically defined in a storage area providedby physical disks (hereinafter referred to as logical volumes) are used.

Also, connected between host apparatuses and external storageapparatuses, a virtualization apparatus is used to provide the hostapparatuses with logical volumes virtually defined in a storage areaprovided by physical disks (hereinafter simply referred to as virtualvolumes).

Examples of a method for backing up data sent from a host apparatus athigh speeds using the above-described apparatuses include the following.

Data sent from a host apparatus is first stored in volumes provided in avirtualization apparatus and logically defined in a storage areaprovided by physical disks (hereinafter simply referred to as logicalvolumes). Then, the data stored in the logical volumes is replicated inother logical volumes via backup processing on a per-volume basis. Thatreplicated data for the data is stored in virtual volumes, but actuallyis stored in logical volumes provided in a storage apparatus connectedexternally to the virtualization apparatus.

Meanwhile, in the backup processing, in order to protect data andachieve improved reliability, several generations of backup data shouldbe created. In common backup processing, backup data is made ininexpensive tape library apparatuses, i.e., replicated data istransferred from a virtualization apparatus to a tape library apparatusvia a backup server, and stored there.

JP11-242570 A discloses techniques for installing a magnetic diskapparatus having magnetic disks and a tape library apparatus in oneexternal storage apparatus, and executing data backup and restorationbetween the magnetic disk apparatus and the tape library apparatus,enabling the realization of efficient management of data storagecapacity and efficient data access.

SUMMARY

Replicated data can be transferred to an externally connected storageapparatus at very high speeds, but physical disks for forming logicalvolumes are expensive. On the other hand, magnetic tapes areinexpensive, but the speeds for transferring replicated data to thosemagnetic tapes are low.

Also, when replicated data is transferred from a virtualizationapparatus to a tape library apparatus via a backup server and a backupof the replicated data is made there, the speed at which the replicateddata is transferred is very low. In addition, there is another problemin that the load on the virtualization apparatus during the backupoperation affects the main operation of the virtualization apparatus.

In particular, when backing up replicated data on a per-file basis inthe situation where several servers are connected, the same number ofbackup servers is required, as there are different types of OS(Operating Systems). So, if backup data is going to be made using abackup server in those circumstances, an expensive and complicatedstructure is required and system management also becomes complicated.

Even when transferring replicated data on a per-file basis directly froman externally connected storage apparatus via a backup server, theoverhead arising from that backup operation inevitably results in lowerbackup performance relative to the backup operation on a per-volumebasis.

The above also applies to restoration processing.

In light of the above, it is an object of the present invention toprovide a storage system and data management method that can reduce theload on a virtualization apparatus by executing backup processing orrestoration processing within one external storage apparatus in whichboth an externally connected storage apparatus and a tape libraryapparatus are installed together.

In order to achieve the above object, the present invention provides astorage system including a virtualization apparatus and an externalstorage apparatus; the virtualization apparatus having: an actual volumefor storing data sent from a host apparatus, formed in a storage areaprovided by a physical disk; and a virtual volume paired with the actualvolume, for storing replicated data for the data, and the externalstorage apparatus having: a logical volume that functions as an actualstorage area for the virtual volume; and a tape associated with thelogical volume, for storing the replicated data, wherein the externalstorage apparatus has a copy unit for copying the replicated data storedin the logical volume to the tape.

Accordingly, it is possible to execute backup processing within theexternal storage apparatus without affecting the virtualizationapparatus.

The present invention also provides a storage system including avirtualization apparatus and an external storage apparatus; thevirtualization apparatus having: an actual volume for storing data sentfrom a host apparatus, formed in a storage area provided by a physicaldisk; a virtual volume paired with the actual volume, for storingreplicated data for the data; and a work virtual volume for storing thereplicated data when it has been copied back for restoration, and theexternal storage apparatus having: a logical volume that functions as anactual storage area for the virtual volume; and a tape associated withthe logical volume, for storing the replicated data; and a work logicalvolume associated with the work virtual volume, wherein the externalstorage apparatus has a controller unit for copying back the replicateddata stored on the tape for restoration in response to a restorationcommand from the host apparatus, and storing the replicated data thathas been copied back in the work logical volume.

Accordingly, it is possible to execute restoration processing on aper-file basis from the work logical volume, in which the replicateddata has been restored at high speeds on a per-volume basis.

The present invention also provides a data management method for astorage system provided with a virtualization apparatus for storing datasent from a host apparatus, and an external storage apparatus connectedto the virtualization apparatus, the method including: a step of thevirtualization apparatus pairing an actual volume with a virtual volume;the actual volume being formed in a storage area provided by a physicaldisk and storing the data, and the virtual volume storing replicateddata for the data; a step of the external storage apparatus associatinga logical volume that functions as an actual storage area for thevirtual volume with a tape for storing the replicated data; and a copystep of the external storage apparatus copying the replicated datastored in the logical volume to the tape.

Accordingly, it is possible to execute backup processing within theexternal storage apparatus without affecting the virtualizationapparatus.

The present invention also provides a data management method for astorage system provided with a virtualization apparatus for storing datasent from the host apparatus, and an external storage apparatusconnected to the virtualization apparatus, the method including: a stepof the virtualization apparatus pairing an actual volume with a virtualvolume; the actual volume being formed in a storage area provided by aphysical disk and storing the data, and the virtual volume storingreplicated data for the data; a step of the virtualization apparatusforming a work virtual volume for storing the replicated data when ithas been copied back for restoration; a step of the external storageapparatus associating a logical volume that functions as an actualstorage area for the virtual volume with a tape for storing thereplicated data; a step of the external storage apparatus forming a worklogical volume associated with the work virtual volume; and a controlstep of the external storage apparatus copying back the replicated datastored on the tape for restoration in response to a restoration commandfrom the host apparatus, and storing the replicated data that has beencopied back in the work logical volume.

Accordingly, it is possible to execute restoration processing on aper-file basis from the work logical volume, in which the replicateddata has been restored at high speeds on a per-volume basis.

According to the present invention, an externally connected storageapparatus and a tape library apparatus are formed as one apparatus, andreplicated data is backed up separately from a virtualization apparatus.As a result, it is possible to reduce the load on the virtualizationapparatus during backup and improve performance in the main operation ofthe virtualization apparatus. It is also possible to improve backupperformance.

Also, according to the present invention, since an externally connectedstorage apparatus and a tape library apparatus are formed as oneapparatus, the devices and software required decrease, resulting in costreduction, and the apparatus reliability can also be improved.

Also, according to the present invention, it is possible to storereplicated data of the latest generation in physical disks while storingthe latest generation and several older generations of that replicateddata on magnetic tapes, resulting in inexpensive and high performancebackup.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the overall configuration of astorage system according to a first embodiment of the invention.

FIG. 2 is a chart showing a generation management table according to thefirst embodiment.

FIG. 3 is a chart showing tape group information according to the firstembodiment.

FIG. 4 is a chart showing a backup target LU table according to thefirst embodiment.

FIG. 5 is a chart showing a path traffic management table according tothe first embodiment.

FIG. 6 is a chart showing a RAID group transfer status table accordingto the first embodiment.

FIG. 7 is a conceptual diagram illustrating the operation of the storagesystem according to the first embodiment.

FIG. 8 is a flowchart illustrating backup processing in a host apparatusaccording to the first embodiment.

FIG. 9 is a sequence chart illustrating backup processing according tothe first embodiment.

FIG. 10 is a flowchart illustrating backup processing in an externalstorage apparatus according to the first embodiment.

FIG. 11 is a flowchart illustrating restoration processing in a hostapparatus according to the first embodiment.

FIG. 12 is a sequence chart illustrating restoration processingaccording to the first embodiment.

FIG. 13 is a block diagram illustrating the overall configuration of astorage system according to a second embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained in detail belowwith reference to the attached drawings.

(1) First Embodiment

-   -   (1-1) Storage System Configuration in the First Embodiment    -   A storage system according to the first embodiment will be        described below.

In FIG. 1, the reference numeral 1 indicates the overall storage systemaccording to the first embodiment. The storage system 1 is configured toinclude a host apparatus 2, a virtualization apparatus 4 connected tothe host apparatus 2 via a network 3, and an external storage apparatus5 connected to the virtualization apparatus 4.

The host apparatus 2 is a computer device provided with informationprocessing resources, such as a CPU (Central Processing Unit) 20 andmemory 21, and it is, for example, a personal computer, workstation,mainframe, or similar. The host apparatus 2 is also provided with aninformation input device (not shown in the drawing), e.g. a keyboard, aswitch, a pointing device, or a microphone, and an information outputdevice (not shown in the drawing), e.g. a monitor display or a speaker.

In the memory 21 of the host apparatus 2, a mirror volume controlprogram 22 and a backup control program 23 are installed, and ageneration management table 24 is also stored, too. Those programs 22and 23, and the generation management table 24 will be explained later.

The network 3 is, for example, a SAN (Storage Area Network), a LAN(Local Area Network), the Internet, a public line, a dedicated line, orsimilar. Communication between the host apparatus 2 and thevirtualization apparatus 4 via the above network 3 is conducted basedon, for example, Fibre Channel Protocol if the network 3 is a SAN, andTCP/IP (Transmission Control Protocol/Internet Protocol) if the network3 is a LAN.

The virtualization apparatus 4 is configured to include a controllerunit 40 and a device unit 41.

The controller unit 40 is configured as a microcomputer system providedwith a CPU 42, memory (not shown in the drawing), a cache 43, and acommunication interface or similar, and controls commands and data sentfrom the host apparatus 2 so that the commands and data are sent andreceived between the host apparatus 2 and the external storage apparatus5.

The cache 43 is mainly used to temporarily store data to be input/outputto/from the virtualization apparatus 4.

The device unit 41 is composed of a plurality of hard disk drives (notshown in the drawing), e.g. expensive hard disk drives such as SCSI(Small Computer System Interface) disks, or inexpensive hard disk drivessuch as SATA (Serial AT Attachment) disks.

In a storage area provided by the above hard disk drives, one or morelogical volumes are defined (not shown in the drawing), and data fromthe host apparatus 2 is read/written from/to the logical volume(s) inblocks of a predetermined size.

Each logical volume is assigned a unique identifier (LUN: Logical UnitNumber). In this embodiment, the above identifier is combined with aunique number assigned to each block (LBA: Logical Block Address) toform an address, and user data is input/output specifying a particularaddress of that type.

The logical volumes formed in the virtualization apparatus 4 includeprimary volumes (PVOLs) and secondary volumes (SVOLs). The secondaryvolumes are logical volumes used for backing up the primary volumes. Ifa failure occurs in a primary volume, that primary volume can be quicklyreproduced using the relevant secondary volume. As for the logicalvolume attribute, there are actual volumes PVOL₀-PVOL_(n) and virtualvolumes SVVOL₀-SVVOL_(n). In this embodiment, the primary volumes aredefined as the actual volumes PVOL₀-PVOL_(n), and the secondary volumesare defined as the virtual volumes SVVOL₀-SVVOL_(n).

The actual volumes PVOL₀-PVOL_(n) are logical volumes to which a certainstorage area has been allocated, so data can be actually input/outputto/from the actual volumes.

On the other hand, the virtual volumes SVVOL₀-SVVOL_(n) are virtuallogical volumes that do not actually exist. Each of the virtual volumesSVVOL₀-SVVOL_(n) is associated with one or more of the actual volumesPVOL₀-PVOL_(n), forming a pair. If data input/output requests aredirected to the virtual volumes SVVOL₀-SVVOL_(n) during backupprocessing or restoration processing executed by the virtualizationapparatus 4, relevant data is read/written from/to any of logicalvolumes LU₀-LU_(n) (explained later) in the external storage apparatus5, which has been associated with the virtual volumes SVVOL₀-SVVOL_(n).

At least one of the virtual volumes SVVOL₀-SVVOL_(n) is assigned as avirtual command volume SVVOL_(m).

In this embodiment, data sent from the host apparatus 2 is stored in anyof the actual volumes PVOL₀-PVOL_(n). The actual volumes PVOL₀-PVOL_(n)are associated with the virtual volumes SVVOL₀-SVVOL_(n), which are alsoassociated with the logical volumes LU₀-LU_(n) (explained later) in theexternal storage apparatus 5, and the replica of the data stored in theactual volumes PVOL₀-PVOL_(n) is stored as the replicated data in therelevant logical volumes LU₀-LU_(n).

The virtual command volume SVVOL_(m) is associated with a logicalcommand volume LU_(m) (explained later) in the external storageapparatus 5. As a result, if a command is given by the host apparatus 2for the virtual command volume SVVOL_(m), that command is transferred tothe logical command volume LU_(m) associated with the virtual commandvolume SVVOL_(m).

The external storage apparatus 5 is configured to include a controllerunit 6, a device unit 7, an FC switch 8, and a tape library 9.

The controller unit 6 is configured as a microcomputer system providedwith a CPU 60, memory 61, and a communication interface or similar, andcontrols commands and data sent/received to/from the host apparatus 2via the virtualization apparatus 4.

The device unit 7 is composed of a plurality of hard disk drives 70,e.g. expensive hard disk drives such as SCSI (Small Computer SystemInterface) disks, or inexpensive hard disk drives such as SATA (SerialAT Attachment) disks.

In a storage area provided by the above hard disk drives 70, one or morelogical volumes LU₀-LU_(n) are defined, and replicated data from theassociated virtual volumes SVVOL₀-SVVOL_(n) is read/written from/tothose logical volumes LU₀-LU_(n) in blocks of a predetermined size. Thelogical volumes LU₀-LU_(n) have the same configuration as that of thelogical volumes PVOL₀-PVOL_(n) in the virtualization apparatus 4, sotheir detailed explanation will be omitted.

A logical command volume LU_(m), which is one of the logical volumesLU₀-LU_(n), is associated with the virtual command volume SVVOL_(m).

The FC switch 8 is a switch connected to the controller unit 6 and thetape library 9 via a network where Fibre Channel Protocol is used, andis used for transferring data via switching. The FC switch 8 transfersreplicated data stored in the logical volumes LU₀-LU_(n) to the tapelibrary 9 via the controller unit 6, using a data transfer path calledpath P.

The tape library 9 is configured to include: tape drives 91; tapecartridges 92; a carrying mechanism 90 for carrying the tape cartridges92; a CPU (not shown in the drawing) for controlling the carryingmechanism 90; and memory (not shown in the drawing) that stores acontrol program for controlling the carrying mechanism 90.

The tape drives 91 are drive units for reading/writing replicated datafrom/to the tape cartridges 92. Using the tape drives 91, replicateddata can be stored on the tape cartridges 92.

The tape cartridges 92 store replicated data stored in the logicalvolumes LU₀-LU_(n).

(1-2) Backup function

-   -   Next, the backup function provided in the storage system 1        according to this embodiment configured as above will be        explained.

The storage system 1 is characterized by storing replicated data of thelatest generation in the logical volumes associated with the virtualvolumes, and also storing several older generations of the replicateddata stored in the above logical volumes on the tapes on a per-volumebasis, thereby enabling the external storage apparatus 5 to executebackup processing internally by itself.

In order to realize the above-described backup function, a mirror volumecontrol program 22 and a backup control program 23 are installed, and ageneration management table 24 is stored, in the host apparatus 2.

Meanwhile, a backup program 62 is installed in the external storageapparatus 5, and tape group information 63, a backup target LU table 64,a path traffic management table 65 and a RAID (Redundant Array ofInexpensive Disks) group transfer status table 66 are also stored in theexternal storage apparatus 5.

In the below explanation, the various tables 24 and 63-66 will beexplained first, and the various programs 22, 23 and 62 will beexplained later.

(1-2-1) Generation management table

As shown in FIG. 2, the generation management table 24 is a table formanaging the source-destination relationship when making backups ofreplicated data within the external storage apparatus 5. The generationmanagement table 24 is composed of a “backup source group number” field24A, a “schedule name” field 24B, and a “backup destination tape groupnumber” field 24C.

The “backup source group number” field 24A stores the number given to agroup formed by dividing the logical volumes LU₀-LU_(n) associated withthe virtual volumes SVVOL₀-SVVOL_(n), which are backup sources thatstore the replicated data.

The “schedule name” field 24B stores information for managing howbackups of the replicated data are updated. For example, if the field24B stores “schedule_day,” it shows that backups of the replicated dataare updated every day, and if the field 24B stores “schedule_week,” itshows that backups of the replicated data are updated every week.

The generation management table 24 shows, for example, that a “backupsource group number” of “1” is associated with the “backup destinationtape group numbers” of “10,” “11,” “12,” and “13,” showing that therelevant replicated data is stored in the tape groups “10”-“13.” Inother words, the number of backups (generations) made for particularreplicated data is four, i.e., four generations in the tape groups “10”to “13.” So, it is possible to manage several generations of replicateddata, by switching the tape cartridges 92 associated with any of thedestination tape group numbers in accordance with the intendedgeneration.

(1-2-2) Tape group information

-   -   As shown in FIG. 3, the tape group information 63 includes        update history information about a backup of the replicated data        made in a particular tape group. The tape group is a group made        by selecting several tape cartridges and putting them together.        The tape group information 63 specifically includes: information        63A, indicating the tape group number; information 63B,        indicating the backup date when the replicated data was backed        up; information 63C, indicating a keyword, which is a random        string set by a user to identify the backup; information 63D,        indicating the number of logical volumes that store the        backed-up replicated data; information 63E, indicating the        logical volume numbers given to the logical volumes that store        the backed-up replicated data; copy status information 63F,        indicating the status (e.g. accessible mode, backup mode,        restoration mode, error mode, or undefined mode) of the logical        volumes that store the backed-up replicated data; and        information 63G, indicating what percent of the backup or        restoration process has been completed.

In particular, the backup date information 63B stores historicalinformation indicating when several generations (backups) of particularreplicated data were updated.

(1-2-3) Backup target LU table

-   -   As shown in FIG. 4, the backup target LU table 64 is a table for        managing backup sources in the external storage apparatus 5,        each source storing replicated data. The backup target LU table        64 is composed of a “logical volume number” field 64A, a “RAID        group” field 64B, and a “backup performance” field 64C.

The “logical volume number” field 64A stores the volume number given toeach of the logical volumes LU₀-LU_(n) formed with the hard disk drives70 in the external storage apparatus 5. The controller unit 6 in theexternal storage apparatus 5 manages replicated data on a per-volumebasis.

The “RAID group” field 64B stores the group number given to each RAIDgroup, to which several logical volumes (LU₀-LU_(n)) belong.

The “backup performance” field 64C stores information about the datatransfer speed (MB/s) when a backup of the replicated data in aparticular logical volume (LU₀-LU_(n)) was previously made in the tapelibrary 9.

(1-2-4) Path traffic management table

-   -   As shown in FIG. 5, the path traffic management table 65 is a        table for managing the amount of replicated data that runs        through a data transfer path between the controller unit 6 and        the FC switch 8. The path traffic management table 65 is        composed of a “path number” field 65A, a “traffic threshold”        field 65B, and a “current traffic” field 65C.

The “path number” field 65A stores the number given to a path P, whichis a data transfer path between the controller unit 6 and the FC switch8. In this embodiment, there are four paths, but the number of paths isnot limited to four.

The “traffic threshold” field 65B stores the maximum transfer rate(MB/s) at which data can be transferred via a particular path P.

The “current traffic” field 65C stores the amount of replicated data(MB/s) currently running through a particular path P.

(1-2-5) RAID group transfer status table

-   -   As shown in FIG. 6, the RAID group transfer status table 66 is a        table for managing the transfer status of the replicated data        stored in the logical volumes (LU₀-LU_(n)) within a particular        RAID group. The RAID group transfer status table 66 is composed        of a “RAID group number” field 66A and a “transfer flag” field        66B.

The “RAID group number” field 66A stores the number given to a RAIDgroup formed by grouping several logical volumes (LU₀-LU_(n)) together.Here, the RAID group is a group prepared so that multiple hard diskdrives can be operated based on RAID.

The “transfer flag” field 66B stores information indicating whether thereplicated data stored in the logical volumes (LU₀-LU_(n)) within aparticular RAID group is being transferred or not. In this embodiment, aflag of “1” is stored if the replicated data is being transferred,otherwise, a flag of “0” is stored.

(1-3) Storage system operation

-   -   Next, how data from the host apparatus 2 is stored and backed up        in the storage system 1 will be explained below. The following        explanation will be made focusing on one actual volume PVOL₀,        one virtual volume SVVOL₀, and one tape cartridge 92, from among        the several volumes PVOL₀-PVOL_(n), virtual volumes        SVVOL₀-SVVOL_(n), and tape cartridges 92.

In the graph shown in FIG. 7, the vertical scale R indicates the load onthe storage system 1, while the horizontal scale T indicates time, e.g.one day or one week. In the graph, the time periods R1 and R3 where theline extends curvedly in the direction of the vertical scale R show ahigh load period, i.e., a time period during which commands and data arebeing sent and received frequently between the host apparatus 2 and thevirtualization apparatus 4 in the storage system 1. Meanwhile, the timeperiod R2 where the line extends straight in the direction of thehorizontal scale T shows a low load period, i.e. a time period duringwhich commands and data are not frequently being sent and receivedbetween the host apparatus 2 and the virtualization apparatus 4 in thestorage system 1.

Above the graph shown in FIG. 7, the flow of data between the actualvolume PVOL0 and the virtual volume SVVOL₀, both in the virtualizationapparatus 4, and the flow of the relevant replicated data between thevirtual volume SVVOL₀ and the tape cartridge 92 in the external storageapparatus 5 are described, the flows varying in accordance with the loadR and time T.

In the high load period R1, which is, for example, during the day, thestorage system is operated, with the actual volume PVOL₀ and the virtualvolume SVVOL₀ in the virtualization apparatus 4 separated from eachother. During this high load period R1, data sent from the hostapparatus 2 is stored in the actual volume PVOL₀ in the virtualizationapparatus 4.

Then, in the low load period R2, which is, for example, during thenight, in order to match the data stored in the actual volume PVOL₀ andthe replicated data stored in the virtual volume SVVOL₀ in thevirtualization apparatus 4, the replicated data is updated by copyingthe difference data between the actual volume PVOL₀ and the virtualvolume SVVOL₀ from the actual volume PVOL₀ to the virtual volume SVVOL₀.In the above process, the replicated data is actually stored in thelogical volume LU₀ in the external storage apparatus 5, which functionsas an actual storage area for the virtual volume SVVOL₀. As a result,the virtual volume SVVOL₀ stores the replicated data of the latestgeneration.

This embodiment employs copying the difference data between the actualvolume PVOL₀ and the virtual volume SVVOL₀, but it is also possible tocopy the incremental data between the actual volume PVOL₀ and thevirtual volume SVVOL₀, and any copy method can be used as long as it canmatch the data in the actual volume PVOL₀ and the data in the virtualvolume SVVOL₀.

If the storage system 1 is again under a high load (high load periodR3), the storage system 1 is operated, with the actual volume PVOL₀ andthe virtual volume SVVOL₀ in the virtualization apparatus 4 separatedfrom each other. After that separation, the replicated data temporarilystored in the cache 43 in the virtualization apparatus 4 is stored inthe logical volume LU₀. After that, using the logical volume LU₀ that isthe actual storage area for the separated virtual volume SVVOL₀, theexternal storage apparatus 5 backs up the replicated data of the latestgeneration stored in the logical volume LU₀ on the tape cartridges 92.

As described above, in the storage system 1 according to thisembodiment, the external storage apparatus 5 can execute backupprocessing internally without affecting the virtualization apparatus 4.

(1-3-1) Backup processing in the host apparatus

-   -   In order to realize the above-described operation of the storage        system 1, the CPU 20 in the host apparatus 2 executes backup        processing based on the mirror volume control program 22 and the        backup control program 23.

More specifically, as shown in FIG. 8, the CPU 20 in the host apparatus2 starts backup processing during the low load period R2, which is, forexample, during the night (SP0). The CPU 20 sends a command instructingpairing of the actual volumes PVOL₀-PVOL_(n) with the virtual volumesSVVOL₀-SVVOL₀ so that the actual volumes are mirrored by the virtualvolumes (SP1). Then, in the virtualization apparatus 4, data sent fromthe host apparatus 2 is stored in the paired actual volumes PVOL₀-PVOL₀,and the replicated data for that data is stored in the relevant virtualvolumes SVVOL₀-SVVOL₀. After that, the CPU 20 instructs deletion of theparing between the actual volumes PVOL₀-PVOL₀ and the virtual volumesSVVOL₀-SVVOL₀ (SP2).

The CPU 20 then sends a cache-purge command so that the replicated datatemporarily stored in the cache 43 in the virtualization apparatus 4 isstored in the logical volumes LU₀-LU_(n) in the external storageapparatus 5, which are associated with the virtual volumesSVVOL₀-SVVOL_(n) (SP3).

After that, the CPU 20 gives the external storage apparatus 5 a commandto back up the replicated data stored in the logical volumes LU₀-LU_(n)(SP4), and ends backup processing on the host apparatus 2—side (SP5).

Note that the CPU 20 executes backup processing via the backup controlprogram 23 in step SP3 above, and via the mirror volume control program22 in the other steps SP1, SP2 and SP4.

(1-3-2) Backup processing between the host apparatus and the externalstorage apparatus

-   -   Next, the sequence where the host apparatus 2 gives a command to        execute backup processing to the external storage apparatus 5,        and in response, the external storage apparatus 5 executes and        completes the backup processing will be explained.

As shown in FIG. 9, when the host apparatus 2 receives a backup commandfrom a user (SP10), the host apparatus 2 sends the external storageapparatus 5 a request for the tape group information 63 (SP11).

When receiving the above request, the external storage apparatus 5 sendsthe tape group information 63 in the memory 61 to the host apparatus 2(SP12).

When obtaining the tape group information 63 sent from the externalstorage apparatus 5 (SP13), the host apparatus 2 starts selecting abackup destination (SP14). More specifically, the host apparatus 2 readsthe generation management table 24, and checks the backup source logicalvolume number(s) and the corresponding backup destination tape groupnumbers. Then, the host apparatus 2 refers to the backup dateinformation 63B in the obtained tape group information 63, selects, fromamong the several candidate backup destination tape group numbers, thetape group having the oldest backup update date, and specifies it as thebackup destination tape group.

When the tape group(s) has been specified, the host apparatus 2 permitsthe external storage apparatus 5 to overwrite the data in the specifiedtape group(s) with the replicated data (SP15). The external storageapparatus 5 receives that permission for overwriting (SP16).

Then, the host apparatus 2 instructs the external storage apparatus 5 tomake a backup of the replicated data and store it in the specified tapegroup(s) (SP17). The backup instruction command includes the logicalvolume number(s), the specified tape group number(s), and the randomkeyword(s) set by the user.

When receiving the backup command from the host apparatus 2, theexternal storage apparatus 5 executes backup processing for thespecified tape group(s) (SP18). The details of the backup processingwill be explained later. When completing the backup processing (SP19),the external storage apparatus 5 updates the tape group information 63(SP20).

Then, the external storage apparatus 5 sends a backup processingcompletion report and the updated tape group information 63 so that thehost apparatus 2 can know of the completion of the backup processing andits status (normal/abnormal completion) (SP21).

When receiving the backup processing completion report and the updatedtape group information 63 (SP22), the host apparatus 2 displays thenormal/abnormal completion of the backup processing (SP23) on the screenof the host apparatus 2, and ends the processing.

(1-3-3) Backup processing in the external storage apparatus

-   -   Next, how the external storage apparatus 5, when it receives a        backup command from the host apparatus 2, executes backup        processing within the external storage apparatus 5 will be        explained. Backup processing is executed by the CPU 60 in the        external storage apparatus 5 using the backup program 62.

As shown in FIG. 10, first, the CPU 60 in the external storage apparatus5 starts backup processing in response to a backup command from the hostapparatus 2 (SP30), and sorts the entries for each RAID group in thebackup target LU table 64 in descending order of backup performance(SP31).

The CPU 60 then initializes the value for the reference pointer, whichis used for the logical volumes LU₀-LU_(n) in the backup program 62,setting the value calculated in the previous processing back to “0”(SP32).

Then, the CPU 60 refers to the RAID group transfer status table 66 forthe status of data transfer for the RAID group that includes the logicalvolume number(s) specified in the backup command from the host apparatus2 (SP33). This is to execute backup processing [for each logical volume]with a certain time lag to achieve the optimum backup performance.

If the CPU 60 finds that the RAID group that includes the specifiedlogical volume number(s) is undergoing data transfer (SP33: YES), itincrements the value of the reference pointer for the logical volumes(that currently points to, for example, LU₀) by one (SP43) to shift thebackup processing target to the next logical volume (e.g. LU1). Afterthat, the CPU 60 executes step SP44 (judging whether to continue backupprocessing for the next logical volume).

On the other hand, if the CPU 60 finds that the RAID group that includesthe specified logical volume number(s) is not undergoing data transfer(SP33: NO), the CPU 60 initializes the value for the reference pointer,which is used for the path(s) P in the backup program 62 (SP34). Then,the CPU 60 refers to the path traffic management table 65, and checkswhether the path traffic will still be less than or equal to the trafficthreshold even if the amount of replicated data to be transferred, whichis stored in the current target logical volume specified, is added tothe value in the “current traffic” field 65C (SP35).

If the CPU 60 finds that the path traffic will exceed the threshold(SP35: NO), the CPU 60 increments the value of the reference pointer forthe path(s) P by one (SP52), and then checks whether all path numbershave been checked (SP53). In this embodiment, since there are fourpaths, the CPU 60 checks all four paths. Also, even if the path traffichas been found to be less than or equal to the threshold (SP35: YES), ifthe CPU 60 finds, in the subsequent checking of whether the requiredtape cartridge(s) 92 are available or not (SP36), that the required tapecartridge(s) 92 are not available (SP36: NO), the CPU 60 executes theabove-explained steps SP52 and SP53 too.

If the CPU 60 finds that some path numbers have not yet been checked(SP53: NO), the CPU 60 checks the next path number with respect towhether the path traffic will still be less than or equal to thethreshold (SP35), so that a particular path P can be specified.

If the CPU 60 finds that all path numbers have been checked (SP53: YES),the CPU 60 then goes to the process in step SP43.

If the CPU 60 finds that the path traffic will still be less than orequal to the threshold, and specifies that path (SP35: YES), the CPU 60then checks whether the tape cartridge(s) 92 necessary for actuallystoring the replicated data are available in the specified tape groupnumber (SP36). If the CPU 60 finds that the tape cartridge(s) requiredfor actual storage are available in the specified tape group number(SP36: YES), the CPU 60 adds the value in the “backup performance” field64C of the backup target LU table 64, which is the value associated withthe current target logical volume number specified, to the value in the“current traffic” field 65C of the path traffic management table 65(SP37).

After that addition, the CPU 60 sorts the entries in the path trafficmanagement table 65 in ascending order of current traffic, for the nextcheck (SP38).

When the CPU 60 specifies a particular path, the CPU 60 then updates theRAID group transfer status table 66 (SP39). More specifically, the CPU60 sets a flag of “1” for the RAID group (e.g. RAID group “0”) thatincludes the specified logical volume(s) (e.g. LU₀-LU₃), to show thatthe RAID group is undergoing data transfer.

After that, the CPU 60 backs up the replicated data stored in thecurrent target logical volume (backup source) on the tape cartridges 92in the specified backup destination (SP40). At that time, the CPU 60measures the transfer rate during that backup process, and makes arecord as backup history.

In addition, at the time of the above backup process, the CPU 60 updatesthe tape group information 63 (SP41). More specifically, the CPU 60updates the backup date information 63B to the date when the currenttarget backup source logical volume has been backed up, and also changesthe copy status information 63F to backup mode. The CPU 60 also updatesthe other items 63C-63E and 63G in the tape group information 63.

Then, in order to delete the current target logical volume for which thereplicated data has already been backed up, the CPU 60 updates thebackup target LU table 64 (SP42). The CPU 60 stores, in the relevant“backup performance” field 64C in the backup target LU table 64, thedata transfer rate at which the replicated data in that logical volumehas been transferred to be backed up on the tape cartridges 92.

When the backup processing for the current target logical volume (e.g.LU₀) has been completed, the CPU 60 then increments the value of thereference pointer for the logical volumes by one (SP43), and shifts thebackup processing target to the next logical volume (e.g. LU₁).

When the CPU 60 moves to the next target logical volume (e.g. LU₁), theCPU 60 checks whether the value of the reference pointer that points tothe logical volume LU₁ exceeds the number of backup target logicalvolumes (SP44). Then, if the CPU 60 finds that the value of thereference pointer (that points to the logical volume LU₁) does notexceed the number of backup target logical volumes (SP44: NO), the CPU60 goes back to step SP33, and continues executing backup processing forthe next target logical volume LU₁. The CPU 60 repeats the processes insteps SP33-SP44 for the target logical volumes (e.g. LU₀-LU₃).

On the other hand, if the CPU 60 has completed backup processing for thetarget logical volumes (e.g. LU₀-LU₃), and if the CPU 60 finds that thevalue of the reference pointer (that points to, for example, LU₄)exceeds the number of backup target logical volumes (SP44: YES), the CPU60 then checks whether the necessary backup processing has beencompleted or not (SP45).

If the CPU 60 finds that the necessary backup processing has not beencompleted (SP45: NO), the CPU 60 goes to step SP49, which will beexplained later.

If the CPU 60 finds that the backup processing has been completed(SP45:YES), the CPU 60 subtracts, from the value in the relevant“current traffic” field(s) 65C of the path traffic management table 65,the value in the “backup performance” field(s) 64C of the backup targetLU table 64 associated with the logical volume number(s) specified(SP46).

After that subtraction, the CPU 60 again sorts the entries in the pathtraffic management table 65 in ascending order of current traffic(SP47).

Also, the CPU 60 updates the RAID group transfer status table 66 (SP48).More specifically, the CPU 60 changes the value in the “transfer flag”field 66B for the RAID group number (e.g. RAID group “0”) that includesthe specified logical volume(s) (e.g. LU₀-LU₃), from “1” to “0.”

After waiting for a certain period of time (SP49), the CPU 60 checkswhether there is any backup target logical volume or not (SP50).

If the CPU 60 finds that there is a backup target logical volume (SP50:YES), the CPU 60 goes back to step SP31 and executes backup processingagain.

On the other hand, if the CPU 60 finds that there is no backup targetlogical volume (SP50: NO), the CPU 60 then checks whether the necessarybackup processing has all been completed or not (SP51).

If the CPU 60 finds that the backup processing has not all beencompleted (SP51: NO), the CPU 60 goes back to step SP45.

If the CPU 60 finds that the backup processing has all been completed(SP51:YES), that means that the replicated data in all of the logicalvolume(s) (e.g. LU₀-LU₃) specified by the host apparatus 2 has beenbacked up on the tape cartridges 92 in all the specified tape groups(e.g. 0-9), so the CPU 60 ends the backup processing (SP54).

The backup processing is executed within the external storage apparatus5 in the above-explained steps, and accordingly, replicated data can bebacked up, without affecting the virtualization apparatus 4.

(1-3-4) Restoration processing in the host apparatus

-   -   Processing for restoring data in the host apparatus 2 using the        replicated data (i.e., processing for returning the replicated        data to the position that it was copied from) after the        replicated data has been backed up and stored on the tape        cartridges 92 in the external storage apparatus 5 as described        above will be explained below. Upon receipt of a user's command,        the CPU 20 in the host apparatus 2 executes restoration        processing in accordance with the mirror volume control program        22 and backup control program 23. Note that if the replicated        data to be used is the replicated data of the latest generation,        the data in the host apparatus 2 can be restored by copying the        replicated data from the virtual volumes (SVVOL₀-SVVOL_(n)), not        the tape cartridges 92.

More specifically, as shown in FIG. 11, the user first judges whether touse the latest generation of replicated data or an older generation ofreplicated data stored on the tapes, to restore data in the hostapparatus 2 (SP61).

If the user has decided to use an older generation of replicated datastored on the tapes (SP61: NO), the CPU 20 in the host apparatus 2deletes the pair setting for the relevant virtual volume (e.g. SVVOL₀)and the corresponding actual volume (e.g. PVOL₀) to separate them fromeach other, the virtual volume being associated with the logical volume(e.g. LU₀) that is the backup source for the target replicated datastored on the tapes (SP62).

After that, the CPU 20 in the host apparatus 2 sends an cache purgecommand to the virtualization apparatus 4 to prevent the replicated datain the cache 43 from being transferred (SP63), and destroys thereplicated data temporarily stored in the cache 43 in the virtualizationapparatus 4.

Then the CPU 20 in the host apparatus 2 instructs the virtualizationapparatus 4 to copy, for restoration, the older generation replicateddata stored on the tape cartridges 92 back to the logical volume LU₀, inwhich the replicated data of the latest generation is currently stored(SP64).

Next, the CPU 20 in the host apparatus 2 sends a command to reset theparing by exchanging the roles of the relevant virtual volume SVVOL₀ inthe virtualization apparatus 4 and the actual volume PVOL₀ paired withthat volume SVVOL₀ to form a new pair, the virtual volume SVVOL₀ beingassociated with the logical volume LU₀ that is the target of therestoration command (SP65). In other words, the CPU 20 in the hostapparatus 2 instructs setting of a new pair between the actual volumePVOL₀ and the logical volume LU₀ that functions an actual storage areafor the virtual volume SVVOL₀, the former as a secondary volume and thelatter as a primary logical volume. Then, the actual volume PVOL₀ resetas a secondary logical volume receives data input/output requests fromthe host apparatus 2.

The CPU 20 in the host apparatus 2 instructs the virtualizationapparatus 4 to copy the replicated data, which has been stored in thelogical volume LU₀ for restoration, to the actual volume PVOL₀ in thevirtualization apparatus 4 (SP66).

In response to the above instruction, the CPU 42 in the virtualizationapparatus 4 copies the replicated data from the logical volume LU_(o) tothe actual volume PVOL₀ in the virtualization apparatus 4, and afterthat, the CPU 20 in the host apparatus 2 again instructs thevirtualization apparatus 4 to again exchange the roles of the actualvolume PVOL₀ and the logical volume LU₀ that functions as an actualstorage area for the virtual volume SVVOL₀, the former as a primarylogical volume and the latter as a secondary volume (SP67), to return tothe original pairing, and ends the restoration processing.

If the user has decided to use the replicated data of the latestgeneration for restoration in step SP61 (SP61: YES), the CPU 20 executessteps SP65-SP67, and ends the restoration processing.

(1-3-5) Restoration processing between the host apparatus and theexternal storage apparatus using tapes

-   -   Next, the sequence where the host apparatus 2 gives a        restoration command to the external storage apparatus 5, and, in        response, the external storage apparatus 5 completes restoration        processing using (backup) data on the tape cartridges 92 will be        explained. In this embodiment, the case where restoration        processing is executed using a keyword designated by a user when        making the backup data is explained, but restoration processing        may also be executed by the user directly specifying a        restoration target tape group number.

As shown in FIG. 12, the host apparatus 2 first receives from a user arestoration command with, as a parameter, the keyword that the userdesignated when making the relevant backup data (SP70), and the hostapparatus 2, in response, sends the external storage apparatus 5 arequest for the tape group information 63 (SP71).

When receiving the above request, the external storage apparatus 5 sendsthe host apparatus 2 the tape group information 63 stored in the memory61 (SP72).

When obtaining the tape group information 63 sent from the externalstorage apparatus 5 (SP73), the host apparatus 2 searches for therestoration source tape group (SP74). More specifically, the hostapparatus 2 searches the “keyword” information 63C included in the tapegroup information 63 for the keyword designated by the user, andspecifies the tape group number associated with the keyword that matchesthe designated one. For example, the tape group “0” is specified as thesource tape group for restoration.

Then, the host apparatus 2 instructs the external storage apparatus 5 tocopy the replicated data in the specified tape group 0 to the relevantlogical volume for restoration (SP75). The above restoration instructioncommand includes the destination logical volume number for restorationand the specified tape group number. For example, the logical volumenumber “0” is the destination and the tape group number “0” isspecified.

When receiving the restoration command from the host apparatus 2, theexternal storage apparatus 5 executes restoration processing using thespecified tape group 0 (SP76). The external storage apparatus 5 copiesthe replicated data of an older generation stored on the tape cartridgesin the specified tape group “0”, to the destination logical volume LU₀for restoration. After that, the external storage apparatus 5 ends therestoration processing (SP77), and then updates the tape groupinformation 63 (SP78).

Then, in order to inform the host apparatus 2 of the completion ofrestoration and the completion status (normal/abnormal), the externalstorage apparatus 5 sends a restoration completion report and theupdated tape group information 63 (SP79).

When receiving the restoration completion report and the updated tapegroup information 63 (SP80), the host apparatus 2 displays thenormal/abnormal completion status of the restoration processing on thescreen in the host apparatus 2 (SP81), and ends the processing.

(1-4) Advantageous effects of the first embodiment

-   -   According to the first embodiment, an externally connected        storage apparatus and a tape library apparatus are formed as one        apparatus, i.e., an external storage apparatus 5. Since the        external storage apparatus 5 backs up replicated data separately        from the virtualization apparatus 4, it is possible to reduce        the load on the virtualization apparatus 4 during backup and        improve performance in the main operation of the virtualization        apparatus 4, and it is also possible to improve backup        performance .

Also, according to the first embodiment, since an external storageapparatus 5 is formed, the devices and software required decrease,resulting in cost reduction, and the apparatus reliability can also beimproved.

Moreover, according to the first embodiment, it is possible to storereplicated data of the latest generation in the logical volumesassociated with the virtual volumes, while storing the latest generationand several older generations of that replicated data on magnetic tapeson a per-volume basis. Accordingly, inexpensive and high performancebackup can be achieved.

(2) Second Embodiment

-   -   (2-1) Storage system configuration in the second embodiment    -   A storage system according to the second embodiment will be        described below.

In FIG. 13, the reference numeral 1′ shows the overall storage systemaccording to the second embodiment. In this embodiment, a work virtualvolume WVVOL having the same capacity as that of the actual volumesPVOL₀-PVOL_(n) is formed in a device unit 41′ of a virtualizationapparatus 4′. Also, a work logical volume WLU that functions as anactual storage area for the work virtual volume WVVOL is formed in adevice unit 7′ in an external storage apparatus 5′. The host apparatus 2makes the work logical volume WLU recognize the OS installed in the hostapparatus 2. Other components correspond to those already described inthe first embodiment, so their explanation will be omitted.

When executing restoration processing using replicated data stored ontape cartridges 92 in the external storage apparatus 5′, the replicateddata is copied to the work logical volume WLU on a per-file basis.

(2-2) Advantageous effects of the second embodiment

-   -   According to the second embodiment, a work logical volume that        can recognize the OS installed in the host apparatus 2, and a        work virtual volume WVVOL are formed, and accordingly,        file-based restoration can be realized.

(3) Other Embodiments

-   -   In the above embodiments, as a unit for executing step SP17, a        copy unit for copying the replicated data stored in the logical        volumes LU₀-LU_(n) to the tape cartridges 92 is provided in the        external storage apparatus 5. However, the copy unit may be        separate hardware.

Also, the external storage apparatus 5′ is provided with the controllerunit 6 that, in response to a restoration command from the hostapparatus 2, copies back the replicated data stored on the tape on aper-file basis for restoration, and stores the replicated data that hasbeen copied back in the work logical volume. However, the controllerunit may be separate hardware.

The present invention can widely be applied in storage systems havingone or more storage apparatuses, or various other types of storagesystems.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having the benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A storage system comprising: a virtualization apparatus having acontrol unit, said control unit setting an actual volume for storingdata sent from a host apparatus, formed in a storage area provided by aphysical disk; and a virtual volume paired with the actual volume, forstoring replicated data for the data; and an external storage apparatushaving a logical volume that functions as an actual storage area for thevirtual volume; and a tape associated with the logical volume, forstoring the replicated data; wherein the external storage apparatus hasa copy unit for copying the replicated data stored in the logical volumeto the tape.
 2. The storage system according to claim 1, wherein thecopy unit executes backup processing for making a backup of thereplicated data stored in the logical volume on the tape, and executesthat backup processing after deleting the pairing between the actualvolume and the virtual volume in the virtualization apparatus.
 3. Thestorage system according to claim 1, wherein the external storageapparatus comprises a controller unit for controlling backup processingexecuted between a plurality of the logical volumes and a plurality ofthe tapes, the controller unit having tape group information formanaging update history concerning backups of the replicated data storedin some or all of the plurality of the tapes, the copy unit executingthe backup processing for one or more of the tapes in accordance withthe tape group information.
 4. The storage system according to claim 1,wherein the external storage apparatus comprises a controller unit forcontrolling backup processing executed between a plurality of thelogical volumes and a plurality of the tapes, wherein some or all of theplurality of the logical volumes forms a RAID group, some or all of theplurality of the tapes forms a tape group, and the RAID group and thetape group are associated with each other via a plurality of datatransfer paths, and wherein the controller unit judges whether toexecute the backup processing to make a backup of the replicated datastored in a backup target logical volume from among the plurality oflogical volumes, in accordance with the data transfer status of thereplicated data stored in the RAID group including that backup targetlogical volume running through the data transfer path, and selects onepath from among the plurality of data transfer paths in accordance withthe amount of replicated data running through each of the data transferpaths.
 5. A storage system comprising: a virtualization apparatus havinga control unit, said control unit: setting an actual volume for storingdata sent from a host apparatus, formed in a storage area provided by aphysical disk; a virtual volume paired with the actual volume, forstoring replicated data for the data; and a work virtual volume forstoring the replicated data when it has been copied back forrestoration; and an external storage apparatus having: a logical volumethat functions as an actual storage area for the virtual volume; a tapeassociated with the logical volume, for storing the replicated data; anda work logical volume associated with the work virtual volume, whereinthe external storage apparatus has a controller unit for copying backthe replicated data stored on the tape for restoration in response to arestoration command from the host apparatus, and storing the replicateddata that has been copied back in the work logical volume.
 6. A datamanagement method for a storage system provided with a virtualizationapparatus having a control unit setting an actual volume for storingdata sent from a host apparatus, and an external storage apparatusconnected to the virtualization apparatus, the method comprising: a stepof the virtualization apparatus pairing an actual volume with a virtualvolume; the actual volume being formed in a storage area provided by aphysical disk and storing the data, and the virtual volume storingreplicated data for the data; a step of the external storage apparatusassociating a logical volume that functions as an actual storage areafor the virtual volume with a tape for storing the replicated data; anda copy step of the external storage apparatus copying the replicateddata stored in the logical volume to the tape.
 7. The data managementmethod according to claim 6, wherein the copy step executes backupprocessing for making a backup of the replicated data stored in thelogical volume on the tape, and executes that backup processing afterdeleting the pairing between the actual volume and the virtual volume inthe virtualization apparatus.
 8. The data management method according toclaim 6, further comprising: a control step of the external storageapparatus controlling backup processing executed between a plurality ofthe logical volumes and a plurality of the tapes, wherein the controlstep manages tape group information for managing update historyconcerning backups of the replicated data stored on some or all of theplurality of the tapes, and wherein the copy step executes the backupprocessing for one or more of the tapes in accordance with the tapegroup information.
 9. The storage system according to claim 6, furthercomprising: a control step of the external storage apparatus controllingbackup processing executed between a plurality of the logical volumesand a plurality of the tapes, wherein some or all of the plurality ofthe logical volumes forms a RAID group, some or all of the plurality ofthe tapes forms a tape group, and the RAID group and the tape group areassociated with each other via a plurality of data transfer paths, andwherein the control step judges whether to execute backup processing tomake a backup of the replicated data stored in a backup target logicalvolume from among the plurality of logical volumes, in accordance withthe data transfer status of the replicated data stored in the RAID groupincluding that backup target logical volume running through the datatransfer path, and selects one path from among the plurality of datatransfer paths in accordance with the amount of replicated data runningthrough each of the data transfer paths.
 10. A data management methodfor a storage system provided with a virtualization apparatus having acontrol unit setting an actual volume for storing data sent from a hostapparatus, and an external storage apparatus connected to thevirtualization apparatus, the method comprising: a step of thevirtualization apparatus pairing an actual volume with a virtual volume;the actual volume being formed in a storage area provided by a physicaldisk and storing the data, and the virtual volume storing replicateddata for the data; a step of the virtualization apparatus forming a workvirtual volume for storing the replicated data when it has been copiedback for restoration; a step of the external storage apparatusassociating a logical volume that functions as an actual storage areafor the virtual volume with a tape for storing the replicated data; astep of the external storage apparatus forming a work logical volumeassociated with the work virtual volume; and a control step of theexternal storage apparatus copying back the replicated data stored onthe tape for restoration in response to a restoration command from thehost apparatus, and storing the replicated data that has been copiedback in the work logical volume.